The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A conventional automatic transmission may include one or more band brakes, friction clutch assemblies and planetary gear assemblies. A band brake includes a band drum coupled to a rotating component such as an element of a planetary gear assembly and surrounded by a brake band that may be tightened about the drum by an actuator to brake the drum and associated component. A friction clutch includes pluralities of interleaved friction plates and reaction plates disposed between an inner hub with which the friction plates rotate and an outer housing with which the reaction plates rotate. Between the clutch hub or housing and other components such as shafts, quills or planetary gear components, it is often necessary to establish a fluid tight seal in order to either separate fluid filled, i.e., wet, areas from dry areas or to establish a flow path for fluid across or between rotating and non-rotating components. This may be achieved by, in the first case, a resilient seal disposed in a channel or groove between the areas or, in the second case, utilizing a pair of resilient seals disposed in grooves on both sides of the flow path to properly direct fluid flow. Also, one or both of the inner hub and outer housing may be coupled to a shaft or quill by splines.
Conventionally, band brake drums, friction clutch hubs and housings and components having surfaces engaged by resilient seals or including splines have been fabricated of various steels due to the strength and durability these materials provide.
While various steels provide the necessary strength and durability, they are not without drawbacks. The primary contemporary issue with such steel components is weight. Since these components are both carried and translated as part of the total vehicle weight and rotate and thus contribute to powertrain energy loss as they are repeatedly accelerated, they twice contribute to fuel consumption. Accordingly, any weight reduction of a rotating component, such as a brake drum, clutch housing or hub, positively affects fuel consumption both from the standpoint of total vehicle weight as well as powertrain efficiency.
A solution to the weight problem is the substitution of a lighter weight material such as aluminum. Aluminum has about one-third the density of steel and exhibits good heat transfer, both characteristics being important and beneficial in transmission applications. However, it has been found that a aluminum band brake drum, an aluminum clutch housing or hub or an aluminum component having splines or a sealing surface is unsuitable because aluminum does not exhibit suitable wear resistance for use as a brake drum, it may not have sufficient strength to transfer torque across a splined interconnection in a transmission and wear resistance in a bushing surface or seal application is also problematic.
Thus, while aluminum is an attractive from weight and energy savings standpoints, due to its limited strength, especially relative to common steels, in applications involving frictional service and relatively high torque levels, aluminum remains an unattractive alternative. The present invention addresses these shortcomings.